Jeremy Corbyn is facing calls to pull out of a fundraising event for the Stop the War coalition, amid controversy over the group's comments on the Paris terror attacks and its attacks on Labour MPs.
The Labour leader - who was the Stop the War's chair prior to his election as party leader in September - is billed to appear as a speaker at a fundraising dinner in London on Friday.
But former shadow cabinet minister Tristram Hunt said the group - which has been linked to various hard left bodies - was a "really disreputable organisation" and urged Mr Corbyn not to go.
The latest controversy came as shadow cabinet ministers sought to play down reports the Labour leader was planning a purge of critics in his top team who defied his wishes by voting for air strikes on Syria in last week's Commons debate.
However many Labour MPs remain concerned after facing a barrage of online abuse and threats of de-selection if they voted for military action by pro-Corbyn supporters.
Stop the War has been among the most strident critics, demanding the sacking of shadow foreign secretary Hilary Benn after he rallied support for air strikes in a barnstorming Commons speech.
The group has also caused outrage with comments suggesting Paris had "reaped the whirlwind" for Western actions in the Middle East and comparing jihadists to the International Brigade volunteers who fought fascism in the Spanish Civil War.
A spokesman for Mr Corbyn confirmed that he planned to go ahead with the engagement. "Stop the War is a democratic campaigning organisation and he has been a long-term supporter," the spokesman said.
However Mr Hunt, who resigned from the shadow cabinet after Mr Corbyn became leader, insisted it would be a mistake for him to go.
"The Stop the War coalition picketed the Labour Party headquarters when we were trying to run a phone-bank for the Oldham by-election so they were preventing the election of a Labour Member of Parliament," he told BBC1's The Andrew Marr Show.
"We have also seen some pretty ugly comments from them about Hilary Benn and the fact that Hilary Benn should be sacked. Also their comments about Islamic State, their comments about how the French almost had it coming to them.
"They are a really disreputable organisation and I would hope that Jeremy would step back and not go to their fundraiser."
Meanwhile, shadow work and pensions secretary Owen Smith dismissed reports that Mr Corbyn was planning to get rid of dissenters in a New Year shadow cabinet reshuffle.
"I think this is just newspaper tittle-tattle. What I've seen of the way Jeremy Corbyn has handled this in shadow cabinet is that he's been very keen to stress respect for the different views," he told BBC1's Sunday Politics programme.
Shadow energy secretary Lisa Nandy - who also voted with Mr Corbyn on Syria - said a purge would be a mistake.
"There is so much happening at the moment it is absolutely essential that the Labour Party looks outwards and takes the fight to the Tories," she told Radio 5 Live's Pienaar's Politics.
However shadow chancellor John McDonnell - Mr Corbyn's closest ally in his top team - said his position had been strengthened by Labour's better-than-expected victory in the Oldham West and Royton by-election.
Writing in The Observer, he made clear that Mr Corbyn remained intent on transforming the Labour Party into "something more akin to a mass social movement", adding "there is no going back".
"The new leader was also elected with an overwhelming mandate on a political programme that seeks to take the party in a direction that reflects the current views of party members," he wrote.